feat(nvim): phase 3 — replace nvim-cmp with blink.cmp and telescope with snacks.picker

Swap the completion engine to blink.cmp v1.x, dropping nvim-cmp,
its eight cmp-* sources, lspkind, and LuaSnip. Swap the picker
to snacks.picker, removing telescope.nvim and six telescope
extensions. LSP capabilities now sourced from blink.cmp; LSP
navigation keymaps and the colorscheme/keymaps/todo pickers move
to Snacks.picker. friendly-snippets is preserved as blink's
snippet source.

lua/absolute/plugins/snacks.lua

@@ -20,6 +20,13 @@ return {
 				warn = "",
 			},
 		},
-		-- picker added in Phase 3
+		picker = {
+			enabled = true,
+			ui_select = true,
+		},
 	},
+	config = function(_, opts)
+		require("snacks").setup(opts)
+		require("absolute.after.snacks")
+	end,
 }